This R21 is written in response to PA-04-146 Pilot and Feasibility Program in Urology. Our broad, long term objectives are to develop a new technology for detecting prostate cancer metastasis to bone and to establish a mechanism for monitoring success of therapy to prevent cancer induced bone loss, We will accomplish this goal by directly quantifying bone metabolism using 41 Ca and accelerator mass spectrometry. Using an animal model of metastatic human prostate cancer developed in our laboratory, we will establish the feasibility of using 41 Ca to diagnose and monitor therapy for bone metastasis. In addition, we will begin human experiments in patients at high risk of developing prostate cancer metastasis to provide the necessary data and experience to justify further human clinical studies (e.g. RO1). Our eventual goal is to gather sufficient data to warrant inclusion of 41 Ca in a multi-site clinical trial examining the use of bisphosphonates in the treatment and prevention prostate cancer metastasis. [unreadable] [unreadable]